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Measurements, ideas, curiosities

Measurements, ideas, curiosities. fundamental limitations to the ultimate performance of high-luminosity colliders. Complement to the lecture on Electron Cloud and Beam-Beam Effects. Electron Cloud build-up and Le Ch â telier’s principle.

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Measurements, ideas, curiosities

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  1. Measurements, ideas, curiosities fundamental limitations to the ultimate performance of high-luminosity colliders Complement to the lecture on Electron Cloud and Beam-Beam Effects Univ. “La Sapienza”, Rome, 20–24 March 2006

  2. Electron Cloud build-up and LeChâtelier’s principle • Henri Louis Le Châtelier (1850-1936) was a French industrial chemist. In 1888 he made a remarkable observation: "If a dynamic equilibrium is disturbed by changing some conditions, the position of equilibrium moves to counteract the change." • In modern accelerators we want to accumulate more and more intense, positive beams. • Nature reacts by the fast build-up of negative electron clouds that tend to neutralize the system! Henri Le Châtelier A man of Principle… Electron Cloud and Beam-Beam Effects

  3. Scaling of electron cloud effects blue: e-cloud effect observed red: planned accelerators experience at several storage rings suggests that the e-cloud threshold scales as Nb~Dtsep possible LHC upgrades consider either smaller Dtsep with constant Nb, or they increase Dtsep in proportion to Nb longer fewer more intense bunches more ‘ultimate’ bunches

  4. Electron-cloud build-up in the LHC • Beam synchrotron radiation is important • provides source of photo-electrons • Secondary emission yield (SEY) d(E) is important • characterized by peak value dmax • determines overall e– density • e– reflectivity d(0) is important • determines survival time of e– • Bunch intensity Nb and beam fill pattern are important • Main concern: power deposition by electrons on the cold beam screen Electron Cloud and Beam-Beam Effects

  5. Secondary Electron Yieldfor normal electron incidence R. Cimino et al.,Phys. Rev. Lett. 93, 014801 (2004) Electron Cloud and Beam-Beam Effects

  6. Electron density [m-3] during the passage of an LHC bunch in a field-free region HEADTAIL simulation, courtesy E. Benedetto Electron Cloud and Beam-Beam Effects

  7. Electron density [m-3] during the passage of an LHC bunch in an SPS dipole (top view) HEADTAIL simulation, courtesy E. Benedetto Electron Cloud and Beam-Beam Effects

  8. Electron flux measured in an SPS dipole (strip detector) with LHC beam at 26 GeV courtesy G. Arduini and M. Jimenez Electron Cloud and Beam-Beam Effects

  9. LHC bunch train at injection in the SPS Qx=26.135 Qy=26.185 ξx=0.15 ξy=0.1 VRF ~ 3 MV dampers on coupling: 0.008 Evolution of bunch length and bunch population for the first and the last bunch in an LHC bunch train of 72 bunches. SPS measurements with electron cloud in Aug 2004. Courtesy G. Rumolo, G. Arduini, and F. Roncarolo. rms bunch length (ns) bunch intensity (au) time (min) time (min) Electron Cloud and Beam-Beam Effects

  10. Beam-Beam tune spread for round beams tune shift from head-on collisions (primary IP’s) tune shift from long-range collisions npar parasitic collisions around each IP increases for closer bunches or reduced crossing angle limit on xHO limits Nb/(ge) relative beam-beam separation for full crossing angle qc conservative value for total tune spread based on SPS collider experience high-lumi in IP1 and IP5 (ATLAS and CMS), halo collisions in IP2 (ALICE) and low-lumi in IP8 (LHC-b) Electron Cloud and Beam-Beam Effects

  11. Beam-Beam tune footprints Comparison of tune footprints, corresponding to betatron amplitudes extending from 0 to 6 s , for LHC nominal (red-dotted), ultimate (green-dashed), and “large Piwinski parameter” configuration (blue-solid) with alternating H-V crossing only in IP1 and IP5. (Courtesy H. Grote) Electron Cloud and Beam-Beam Effects

  12. Long-Range Beam-Beam Experiment in RHIC, 28 April 2005,Wolfram Fischer et al. • Effects of long-range beam-beam interaction observable at RHIC injection energy (24.3 GeV) with a single proton bunch per ring • Bunch intensity Nb~1-21011 Electron Cloud and Beam-Beam Effects

  13. Long-Range Beam-Beam Experiment in RHIC, 28 April 2005,Wolfram Fischer et al. collision at s=10.65m 1 bunch per ring Blue beam moved vertically Tunes: B (0.739,0.727) Y (0.727,0.738) Beam losses increase when the beam-beam separation at a single parasitic collision point is reduced below ~5 s. Electron Cloud and Beam-Beam Effects

  14. Electron Cloud: recent links & references http://ab-abp-rlc.web.cern.ch/ab-abp-rlc-ecloud/ (web site on Electron Cloud Effects in the LHC) http://icfa-ecloud04.web.cern.ch/icfa-ecloud04/ (ECLOUD’04 workshop, Napa, California, 19–23 April 2004) http://www-project.slac.stanford.edu/ilc/testfac/ecloud/elec_cloud.html (web site of ILC Damping Ring Task Force 6) “Can low energy electrons affect high energy physics accelerators?”, R.Cimino, I.R. Collins, M.A. Furmann, M. Pivi, F. Ruggiero, G. Rumolo, and F.Zimmermann, Phys. Rev. Lett. 93, 014801 (2004) “Simulation study of electron cloud induced instabilities and emittance growth for the CERN Large Hadron Collider proton beam”, E. Benedetto, D.Schulte, F.Zimmermann, and G. Rumolo, Phys. Rev. ST Accel. Beams8, 124402 (2005) “Update on electron-cloud power deposition for the Large Hadron Collider arc dipoles”, M. Furmann and V.H. Chaplin, LBNL-59062/CBP Note 723/LARP-doc-157, March 2006, to appear in Phys. Rev. ST Accel. Beams Electron Cloud and Beam-Beam Effects

  15. Beam-Beam: recent links & references http://wwwslap.cern.ch/collective/zwe/lhcbb/ (web site of LHC Beam-Beam studies) http://www.agsrhichome.bnl.gov/AP/BeamBeam/Workshop03/ (Beam-Beam Workshop, Montauk, Long Island, 19–23 May 2003) “Coherent beam-beam modes in the LHC for multiple bunches, different collision schemes and machine symmetries”, W. Herr and T. Pieloni, Proc. CARE HHH-2004 Workshop, CERN, 8–11 November 2004 “Progress of Beam-Beam Compensation Schemes”, F.Zimmermann and U.Dorda, Proc. LHC-LUMI-05 Workshop, Arcidosso, 31 Aug–3 Sept 2005 “Beam-beam effects in the Tevatron”, V. Shiltsev, Y. Alexahin, V.Lebedev, P.Lebrun, R.S. Moore, T. Sen, A. Tollestrup, A. Valishev, and X.L. Zhang, Phys. Rev. ST Accel. Beams 8, 101001 (2005) “The effects of solenoids and dipole magnets of LHC experiments”, W.Herr, LHC Project Workshop, Chamonix XV, 23-27 January 2006 Electron Cloud and Beam-Beam Effects

  16. CERN Accelerator Complex (not to scale) Electron Cloud and Beam-Beam Effects

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